1. Field of the Invention
The present invention relates to a radiation imaging system and assist apparatus for the same. More particularly, the present invention relates to a radiation imaging system in which radiation from a radiation apparatus is detected by a radiation detection apparatus for imaging of a body, and an angle of the radiation apparatus can be precisely controlled, and assist apparatus for the same.
2. Description Related to the Prior Art
Long region imaging or image production for a large area image is known and used in medical imaging to observe an area of a full spine or full leg of a body of a patient, mainly in order to measure various bones. The use of a long imaging plate cassette (IP cassette) and a long film is known as a radiation detection apparatus. A distance (SID or source image distance) from an X ray source or radiation source to the radiation detection apparatus is determined as a large value to cover the entire area of imaging. This is effective in forming a long region image or stitched image only by one operation of imaging.
An FPD device (flat panel detector) as radiation detection device has been widely used as one example of the radiation detection apparatus, and receives transmitted X rays or radiation and converts this directly into data of a digital image. However, it is extremely difficult to construct the FPD device in a large size in contrast with the long imaging plate cassette (IP cassette) or long film. A largest size of a known type of the FPD device is 17 inches×17 inches. JP-A 2005-270277 discloses a technique for the long region imaging of the full spine or full leg even by use of the FPD device. An entire area of imaging is split in plural element areas of image positions, in which the body is imaged for plural times. Component images are formed from the image positions, and combined to form the long region image by image stitching.
In the long region imaging with the FPD device, it is necessary to move the X ray source by following the motion of the FPD device for radiation or X rays from the X ray source to become exactly incident on a detection area on the FPD device. Two types of mechanisms for moving the X ray source are known, including a translational motion mechanism and a rotational motion mechanism. The translational motion mechanism moves the X ray source linearly in response to motion of the FPD device. The rotational motion mechanism changes the angle of the X ray source to change an angle of the radiation or X rays in response to the motion of the FPD device.
It has been known that the rotational motion mechanism is more preferable than the translational motion mechanism for the reason of image stitching of component images of adjacent ones of the image positions. See U.S. Pat. No. 5,485,500 (corresponding to JP-A 7-059764). This is because the radiation incident upon the FPD device is not parallel beams but diffusive beams which initially travel from a focal point of the X ray source. In the translational motion mechanism, positions of focusing of the radiation are different between the image positions. There is a difference in an incident angle of the radiation between the component images within overlapping regions between adjacent ones of the component images. There occurs a problem in low precision in the matching of the component images in the overlapping regions. The long region image from the translational motion mechanism has a low quality in the continuous property between the component images in the overlapping regions. In contrast, in the rotational motion mechanism, a focal point of the radiation is fixed. An angle of the radiation is only changed. No difference occurs in the incident angle of the radiation within the overlapping regions. The long region image will have high precision in the matching of the component images in the overlapping regions.
In the most widely available types of radiation imaging system in clinics, hospital or other medical facilities, there is no function for the long region imaging. Instead, an auto tracking function is used, in which the X ray source is linearly moved by following the position of the FPD device as designated by an operator. In the auto tracking function, a position of the FPD device is detected by a position sensor such as a potentiometer. An output from the position sensor is input to a controller for the X ray source according to an analog connection or retro connection on a signal line. The auto tracking function is possible only when an optical axis of the X ray source is horizontal.
In general, the X ray source can be adjustable manually for a change in the angle suitably for the upright posture or supine posture of a body. Even in the radiation imaging system only with the auto tracking function, the long region imaging with the rotational motion mechanism is possible by disabling the auto tracking function and by manually adjusting a position of the FPD device and a position and angle of the X ray source. However, the adjustment for each of events of forming a component image will take long time. Problems arise in that speed of radiation imaging will be low to lower efficiency, and that physical stress of the patient will increase considerably.